Can they tell if my aunt was killed by an autopsy?

My 34 year old aunt died on sep 13 2010 by some how falling or being pushed over an overp on to the high way below. That alone didnt kill her but by a 18 wheeler that hit her and didnt stop then by a car then a truck and then 2 more 18 wheelers. Her body was turn and draged more then 400 ft so i am wondering is it possible that an autopsy can show a fight or something before. We think some one did thins to her since she was about to get ALOT of money and her boyfriend was abusive and needed the money to pay back childsupport that they had been fighting over. The cops havent even talked with him after us calling them many times to do so also only 2 cars stoped on to help my aunt before she died but couldnt get to her before the 18 wheeler then the car that hit her soon later.